feat: Add Dragonfly vector database cookbook with hybrid search examples - #48

Copied from upstream: openai/openai-cookbook#1976
Original author: @vyavdoshenko
Originally opened: 2025-07-28

Summary

This PR introduces a comprehensive Dragonfly vector database cookbook with practical examples of vector similarity search and hybrid queries using OpenAI embeddings, plus improvements to the Redis examples.

Motivation

This addition makes Dragonfly accessible to OpenAI Cookbook users and provides a practical alternative to Redis for vector database use cases, while also improving the Redis examples with proper dependency management.

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